Air diffusers comprising blocks of wood have been used for many years in the operation of co-current and counter-current foam fractionators. The wood blocks are typically of basswood (limewood) or oak with a drilled hole extending from an end face of the block perpendicularly to the normal grain of the wood. The drilled hole does not pierce the opposite end face of the block. An air fitting allowing connection to a positive pressure air supply is inserted in the open end of the drilled hole. Air under pressure injected into the block through the air fitting follows the normal grain of the wood and exists the block from both end faces in the form of small bubbles. In saltwater, these bubbles are usually very small, e.g. less than about 1 mm in diameter.
A major problem with conventional wood air diffusers is their inability to produce copious amounts of small diameter bubbles for an extended period of time, thereby necessitating frequent replacement. The primary cause of this problem is the lack of uniform distribution of air flowing through the wood block. With the end faces of the block being straight and the drilled hole being circular in cross section, the shortest path for air to flow from the drilled hole to the closest location on an end face of the block is the path of least resistance to air flow. Continued airflow concentrated along this short pathway and the presence of saltwater causes the block to deteriorate over time, resulting in the production of fewer bubbles and increased bubble size. This results in reduced levels of protein removal in foam fractionators because protein, which is attracted to an air-water interface, has a greatly reduced surface to cling to with larger bubbles compared to more smaller bubbles for a given volume of air.
It is therefore an object of the invention to provide a wood air diffuser which has a longer operating life and continues to produce an adequate number of small bubbles during its operating life.